Dynamics of Different Exoelectrogenic Bacteria Predict Performance of Microbial Fuel Cells Used for Wastewater Treatment

Microbial fuel cells (MFCs) have received much attention as an alternative technology that generates electricity simultaneously with wastewater treatment. MFC`s are based on an electrochemically-active biofilm that develops on the anode`s surface, transferring electrons to the anode extracellularly (EET). For MFCs to become a cost-effective wastewater treatment technology, they must produce a stable electro-active microbial community quickly. In order to shorten startup times, temporal studies of anodic-biofilm development are required, however, frequent sampling may reduce functionality of the system due to electroactive-biomass loss; therefore, on-line monitoring of the microbial community without interfering with the system`s stability is essential. By following the anodic-biofilm and planktonic-cells communities, we found that although all anodic-biofilms were composed of similar exoelectrogenic bacterial families, MFCs differed in startup times. Generally, a Desulfuromonadaceae-dominated-biofilm was associated with faster startup-MFCs. Since electroactive taxa are of low abundance in the planktonic phase, they would have no effect on the overall diversity; yet, our results suggests that planktonic-cell concentrations of these bacteria followed a similar trend as the anodic-biofilm and they could therefore serve as a biomarker for monitoring its formation. Additionally, we successfully isolated a novel electroactive species, closely related to Desulfuromonadaceae, and showed that its direct application to the MFC anode rapidly generates high voltage. However, the immediate voltage produced was not stable, suggesting that the isolate`s ability to perform EET under MFC-conditions after growing on a Petri dish was limited. To better understand the inoculation process using this approach, raw wastewater and filtered wastewater were supplemented as an inoculum. Interestingly, the supplemented wastewater led to a substantial reduction of startup times from 20 to 3 days by directly applying Desulfuromonadaceae on the anode.